From the July 10, 1937, issue

EGGS OF OPOSSUM PHOTOGRAPHED TO SHOW EARLIEST LIFE STAGES

Eggs of a very primitive type of mammal, the common American opossum, have been studied and photographed by Dr. Carl Hartman and his associates of the Department of Embryology, Carnegie Institution of Washington, D.C., in their Baltimore laboratory. They have succeeded in obtaining these early life stages at several points of development, from unfertilized and just-fertilized eggs to the earliest divisions of the body into the beginnings of nervous system, muscles, etc.